SLO County could get even more rain, with temps warming back up by the end of the week

Historically, rain in May is not that unusual along the Central Coast.

At Cal Poly, home of climatology for San Luis Obispo, the average May rainfall amount decreases to 0.4 inches from 1.5 inches in April. At the Santa Maria Airport, the average in April is 1.1 inches, decreasing to 0.30 inches in May.

With that said, our weather forecast is predicting a late-season 538 decameter upper-level low-pressure system out of the Gulf of Alaska to move southeastward through Northern California. The associated cold front will swiftly pass through the Central Coast on Saturday afternoon and night, bringing with it moderate to fresh (13 to 24 mph) southerly winds, increasing clouds, and rain.

Our forecast indicates rainfall amounts ranging between 0.10 and 0.33 inches, with the highest amounts in the northwesterly regions (Ragged Point, San Simeon and Cambria) of San Luis Obispo County, and about 0.10 inches in northern Santa Barbara County. Rocky Butte, near Hearst Castle, could receive as much as 0.5 inches.

Snow levels will lower to 5,000 feet, with daytime temperatures only reaching the high 50s. The snow level in Sierra Nevada is forecast to drop to 3,500 feet, with 8 to 12 inches of new snow later Saturday into Sunday.

In the cold front’s wake, be prepared for strong to gale-force (25 to 38 mph) northwesterly winds, partly cloudy to mostly clear skies, and below-average temperatures from Sunday through Tuesday. There is a possibility that the northwesterly winds could escalate to moderate gale-force to fresh-gale force (32 to 46 mph) levels in the coastal regions on Monday and Tuesday. Temperatures will gradually warm over this period; however, the winds will create a chill.

On Wednesday the northwesterly winds will decrease and the coastal valleys (San Luis Obispo) will warm to the mid-70s, while the inland valleys (Paso Robles) the high 70s. The coastal communities will reach the mid-60s but will experience a drop in temperature during the afternoon; however, the southerly facing beaches of Caucus, Avila Beach and Shell Beach will warm up to the low 70s.

Similar to last week, a trough of low pressure will form along the California coastline from Thursday through next Saturday.

This will lead to gentle winds and the formation of a deep and persistent marine layer. This layer will bring pockets of drizzle and fog overnight along the beaches and the coastal valleys, while the coastal valleys will clear during the afternoon, with many of the beaches remaining overcast.

Another round of strong to gale-force (25 to 38 mph) northwesterly winds are forecast next Sunday through most of the following week.

Surf report

A 6- to 8-foot northwesterly (310-degree deep-water) sea and swell (with a 5- to 8-second period) is expected on Sunday, building to 7- to 9-feet (with a 5- to 13-second period) on Monday. This northwesterly sea and swell will further increase to 8- to 10-feet with the same period on Tuesday, decreasing to 6- to 8-feet on Wednesday.

A 4- to 6-foot northwesterly (290-degree deep-water) swell (with an 8- to 11-second period) will develop on Thursday, decreasing to 3- to 4-feet on Friday into next Saturday.

Combined with this northwesterly sea and swell, will be 1- to 2-foot southern hemisphere (205-degree deep-water) swell (with a 15- to 17-second period) on Tuesday through Thursday.

Seawater temperatures will decrease to 50 and 52 degrees through next Saturday.

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

John Lindsey is a retired PG&E marine meteorologist. Email him at JohnLindseyLosOsos@gmail.com or follow him on Twitter @PGE_John.